1. Field of the Invention
This invention relates to a method of making a semiconductor device and a light-sensitive etching agent. More particularly, this invention is concerned with a method whereby a pattern for semiconductor elements is made using a semiconductor silicon substrate having a protective film.
2. Description of the Prior Art
It is well known in the fields of integrated circuits or semiconductors to make a pattern on a semiconductor substrate of a semiconductor element or on the protective film on the semiconductor substrate. The most commonly used method consists in forming a silicon dioxide film on a surface of silicon or germanium, applying thereto a light-sensitive material, for example, a light-sensitive polymer (a photoresist), irradiating and hardening the polymer through a photomask, removing the non-irradiated area, i.e., the non-hardened area, and thus exposing the surface of the silicon dioxide film to make a pattern. The exposed area is then treated with an etching solution for the silicon dioxide film to expose the silicon or germanium substrate. After removing the hardened photoresist, another metal is diffused to the exposed area of silicon or germanium.
The above described photographic technique is known as "photoetching" in general. The diffusion operation is repeatedly carried out depending on the kind of semiconductor element to be produced and correspondingly, the steps of coating of the light-sensitive material, irradiation, development, etching of the silicon dioxide, removing of the light-sensitive material on the non-irradiated area and diffusion must be repeated. Therefore, many hours and precise techniques are required and the hardened area is somewhat weakened in removing the non-hardened area.
Improvements relating to photoetching techniques have been disclosed in U.S. Pat. Nos. 3,095,332, 3,095,341, 3,122,463, 3,346,384, 3,471,291, 3,489,564, 3,494,786, and 3,520,684 - 7, and French Pat. No. 1,394,467. Based on these disclosures, a method of forming a pattern on a film of silicon dioxide on a silicon semiconductor substrate, such as silicon, will be illustrated. A silicon slice having a silicon dioxide film is contacted with an atmosphere of a composition that yields upon irradiation a substance capable of etching the silicon dioxide film with the irradiation being through a photomask having a suitable pattern to thus etch the silicon dioxide film and to form a corresponding pattern in depth. That is to say, the irradiation and etching are carried out at the same time. For example, a silicon slice having a silicon dioxide film is contacted with a gaseous atmosphere such as a fluorine compound capable of yielding fluorine upon irradiation with light, for example, F.sub.2 O, with the irradiation being through a photomask. Alternatively, such a silicon slice is contacted with a gaseous atmosphere of a fluorine compound, for example, fluorobenzene, cooled to form a liquid film of fluorobenzene on the silicon dioxide film and then irradiatd through a photomask. In other examples, a mixture of an organic fluorine compound and mineral acid is used as a liquid etching agent and a mixture of an organic fluorine compound, an organic solvent and polyvinyl alcohol, and optionally with a mineral acid, is used as a solid etchant.
In these methods, however, it is very difficult to effect the reaction of the silicon dioxide film with the fluorine, as a photodecomposition product, uniformly over the entire surface of a pattern in a short time since the fluorine is in a flowing condition and to reproduce the pattern precisily because the fluorine compound is continuously fed between the silicon dioxide film and the photomask when carrying out the contacting in a liquid or gaseous state.
In the formation of a liquid film, furthermore, there is the problem of the surface tension between the liquid and the silicon dioxide film and the problem of how to store the liquid film on the film of silicon dioxide, which will cause various difficulties when the surface is irradiated with light. In view of U.S. Pat. No. 3,494,768, for example, it is not easy to find a method for effecting cycling of the liquified non-exposed gas and the removal of the liquid film containing the fluorine reacted with the silicon dioxide film uniformly over the entire surface to be etched and to devise an apparatus for practicing the method. In addition, during irradiation, the gas and liquid flowing between the photomask and the silicon dioxide film interfere with the light path and the precision of the pattern is lowered greatly. In this system, therefore, it is difficult to increase the precision of a fine pattern required for an IC or a LSI.
We, the inventors, have already reported that a pattern of an oxide film having a thickness is formed in a shortened time by providing on a silicon substrate a single film of a silicon compound such as silicon oxide, silicon nitride, a borosilicate glass or a phosphosilicate glass, or a composite film of two of these materials, applying to the film a composition called a "light-sensitive etching agent" which is decomposed upon irradiation with light to form a material capable of etching the above described oxide film or nitride film with or without another material, drying to form a solid film and then irradiating the light-sensitive etching agent through a photomask having a particular pattern.
According to this method, a quite excellent pattern can be obtained in a short time in comparison with the prior art methods, but it is desirable to be able to produce a more precise pattern in an even shorter time.
It is an object of the invention to produce a semiconductor device having a protective film on a silicon substrate in a short time.
It is another object of the invention to provide a light-sensitive etching agent for producing a semiconductor device in a short time.